Frequency conversion circuits

ABSTRACT

A frequency conversion circuit having first and second input signal terminals, and first and second output terminals includes a plurality of non-linear elements, each one having a pair of input electrodes and an output electrode. The first input electrode of each non-linear element is successively interconnected by a two port input coupling means, said input coupling means having a first end coupled to the first input signal terminal and a second end terminated in a terminating impedance. The output electrode of each non-linear device is successively interconnected by a two port output coupling means coupled between the pair of output terminals. An input signal is fed to the first input signal terminal and is coupled to the input coupling means and a portion of such signal is fed to the first input electrode of each non-linear device. Each portion of the input signal is provided with a successive phase shift as it propagates along the input coupling means. The second input signal terminal is fed by a second signal which is fed to the second input electrode of each non-linear element. In response to the pair of input signals, an output signal is provided at the output electrode of each one of said non-linear devices having frequency components equal to the sum and difference of the frequencies of the first and second input signals. In a preferred embodiment, the frequency propagation characteristics of the output coupling means are selected to support propagation of a first one of said sum and difference frequency components of the output signal.

BACKGROUND OF THE INVENTION

This invention relates generally to radio frequency circuits and moreparticularly to frequency conversion circuits.

As is known in the art, frequency conversion circuits provide an outputsignal in response to an input signal having a frequency which is higheror lower than the frequency of the input signal. One type of frequencyconversion circuit is the so-called down converter or a mixer. Radiofrequency mixer circuits are widely employed in superheterodynereceivers which include in addition to the mixer an intermediatefrequency (IF) amplifier tuned to a predetermined frequency providedfrom the mixer and a fixed frequency detector which is fed the amplifiedsignal from the IF amplifier. Generally, a received input signal and alocal oscillator (LO) signal are fed to the mixer circuit to provide anoutput signal having a pair of frequency components equal to the sum anddifference of the frequencies of the input signal and the localoscillator signal. Typically, the sum frequency component is filteredfrom the signal and the signal having the difference frequency componentis fed to the IF amplifier.

One type of mixer is the so-called single-ended mixer. The single-endedmixer generally includes a nonlinear device such as a transistor or adiode which is fed by the input signal and the local oscillator signal.In response an output signal is provided having the sum and differencepair of frequencies (i.e., ω_(rf) ±ω_(LO)).

One problem with this type of mixer, however, is that the output signalgenerally includes undesirable frequency components such as the inputsignal frequency ω_(rf), the local oscillator signal frequency ω_(LO),harmonics (nω_(rf), mω_(LO)) of the original input signals,intermodulation products of the harmonics (m ω_(LO) ±nω_(rf)), and a DCoutput level. It is generally required to suppress the undesiredfrequency components, since their presence may cause frequency ambiguityin the receiver. A second problem with single-ended mixers is that thelocal oscillator signal terminal and the radio frequency input signalterminal generally are not isolated. Thus, a portion of the localoscillator signal may feed through to the radio frequency terminalcausing radiation of the local oscillator signal and additionalinterference problems.

A further problem with the single-ended mixer is the so-called imageresponse of the mixer. The desired IF frequency ω_(IF) can be producedby an r.f. signal having a frequency above or below the frequency of thelocal oscillator (ω_(rf) =ω_(LO) ±ω_(IF)). If one of the IF frequenciesis the desired frequency, then the other frequency is termed the imagefrequency. If one input signal produces the desired IF signal, then theother input signal produces a signal referred to as the image signal. Inmany applications, it is necessary to either distinguish between thedesired and image signals or eliminate the image signal. With asingle-ended mixer, there is generally no way to distinguish between thedesired signal and the image signal; therefore, filtering is employed toeliminate the image signal. Fixed frequency filtering, however, ispossible only when there is no overlap in the bandwidth of the desiredsignal and the image signal and tunable frequency filtering aregenerally difficult to fabricate over wide bandwidths, particularly, asintegrated circuits. Therefore, for broadband applications, filtering isgenerally not successfully employed with single-ended mixers.

A third problem with the single-ended mixer is that the mixer not onlyresponds to a signal at the image frequency, it may produce a signal atthe image frequency. The mixer generally produces such a signal in oneof two ways: First, an r.f. signal having a frequency higher or abovethe local oscillator frequency (given by ω_(rf) =ω_(LO) +ω_(IF)) ifmixed with the second harmonic of the local oscillator signal 2 _(LO)will produce a signal at the image frequency (ω_(IM)) (given by ω_(IM)=2ω_(LO) -ω_(rf)).

Alternatively, an impedance mismatch at the IF output terminal willproduce a reflected signal which will propagate back towards the mixer.This reflected signal mixes with the local oscillator signal to producea signal either above or below the local oscillator signal (ω_(LO)±ω_(IF)), one of which is at the image frequency. Nevertheless, ineither case, the signal produced at the image frequency increases theconversion loss of the mixer, or in other words, reduces the efficiencyby which the mixer converts the input signal to the desired IF signal.

A second type of mixer is the so-called balanced mixer. A balanced mixergenerally includes a pair of single-ended mixers and a 3 db hybridcoupler. The inputs of the coupler are fed the input signal and localoscillator signal and outputs of the hybrid are coupled to the input ofeach single-ended mixer. The outputs of the mixer elements are combinedin a common junction to provide the output IF signal. The balanced mixergenerally has a relatively high isolation between input and localoscillator signals if the outputs of the hybrid are properly terminatedthereby reducing re-radiation of the LO signal. The hybrid provides apredetermined phase shift between the input signal and local oscillatorsignal generally equal to 90° or 180°. Balanced mixers having a 90°phase shift between the local oscillator signal and the input signal aregenerally used to suppress harmonics and intermodulation products forboth the input signal and the local oscillator signal. Balanced mixershaving a 180° phase shift between the signals are generally used tosuppress the even harmonics of the local oscillator frequency signal.One problem with either of the balanced mixers is that while theabove-recited balanced mixer configurations suppress some of theunwanted frequency components in the output, certain others of thosefrequency components are not suppressed. A second problem is that thebalanced mixer includes a hybrid coupler, a generally difficult circuitto fabricate, particularly as an integrated circuit. Furthermore, thebalanced mixer may produce energy at the image frequency. Also, thebalanced mixer cannot differentiate between input signals havingfrequencies either above or below that of the local oscillator signal.Further still, since the balanced mixer requires the use of a hybridcoupler, the bandwidth of the balanced mixer is generally limited due tothe limited bandwidth of the hybrid coupler.

A third type of mixer is the so-called double balanced mixer. The doublebalanced mixer generally includes two balanced mixers, each fed by thelocal oscillator signal and one of a pair of input signals having a 180°differential phase shift provided by a hybrid coupler or balun. Theoutputs of each balanced mixer are combined together by an IF hybridcoupler. One problem with double balanced mixers is that the couplers orbaluns are generally difficult to fabricate as monolithic integratedcircuits. Accordingly, the double balanced mixer is not easilyfabricated as a monolithic integrated circuit. A second problem with thedouble balanced mixer is a relatively narrow frequency bandwidth ofoperation of the mixer due to the presence of the couplers and baluns.Further, while certain configurations of double balanced mixers maydistinguish between signals having a frequency either higher or lowerthan that of the local oscillator, those configurations of the doublebalanced mixers may still produce a signal at the image frequency.

As is also known in the art, a second type of frequency conversioncircuit, an up converter, provides an output signal having a frequencywhich is higher than the frequency of the input signal. As mentionedabove, a nonlinear device when fed input and local oscillator signals,provides an output signal having frequency components equal to the sumand difference between the frequencies of said signals. Therefore, byfiltering the difference frequency component, the remaining sumfrequency component provides a signal having a frequency which is higherthan the frequency of the input signal.

SUMMARY OF THE INVENTION

In accordance with the present invention, a frequency conversion circuithaving first and second input signal terminals, and first and secondoutput terminals includes a plurality of nonlinear elements, each onehaving a pair of input electrodes and an output electrode. The firstinput electrode of each nonlinear element is successively interconnectedby a two port input coupling means, said input coupling means having afirst end coupled to the first input signal terminal and a second endterminated in a terminating impedance. The output electrode of eachnonlinear device is successively interconnected by a two port outputcoupling means coupled between the pair of output terminals. An inputsignal is fed to the first input signal terminal and is coupled to theinput coupling means and a portion of such signal is fed to the firstinput electrode of each nonlinear device. Each portion of the inputsignal is provided with a successive phase shift as it propagates alongthe input coupling means. The second input signal terminal is fed by asecond signal which is fed to the second input electrode of eachnonlinear element. In response to the pair of input signals, an outputsignal is provided at the output electrode of each one of said nonlineardevices having frequency components equal to the sum of the frequenciesof the first input signal and the difference in frequency between theinput signals. In a preferred embodiment, the frequency propagationcharacteristics of the output coupling means are selected to supportpropagation of a first one of said sum and difference frequencycomponents of the output signal. With such an arrangement, a frequencyconversion circuit is provided having a frequency characteristicselected in accordance with the frequency propagation characteristics ofthe output coupling means. This generally results in elimination orreduction of external filtering requirements.

In accordance with a further aspect of the present invention, theplurality of nonlinear elements include a transistor biased, forexample, to operate as a half-wave vth law device, such as a half-wavesquare law device. Preferably, each transistor is a field effecttransistor having the pair of input electrodes, the output electrode anda reference electrode. Each transistor has the first input electrodeinterconnected by the input coupling means and the output electrodesuccessively interconnected by the output coupling means. The inputcoupling means is fed the first input signal and provides signals eachhaving a successively increasing phase shift which are fed to the firstinput electrode of each transistor. The second input electrode of eachtransistor is fed an equal amplitude, in-phase portion of the second orlocal oscillator signal. In response, output signals from each outputelectrode are coupled to the output coupling means having frequencycomponents equal to the sum of and difference between the frequencies ofthe input and local oscillator signals. The propagation characteristicsof the output coupling means are selected to support propagation of oneof the sum and difference frequency components and provide apredetermined phase shift to each of the output signals. The phaseshifts from the input and output coupling means are selected to have theoutput signals from each output electrode add in-phase at a first outputterminal and provide a null or attenuated signal at the second outputterminal, in accordance with, the frequency of the input signal withrespect to the frequency of the local oscillator signal. Accordingly,the mixer circuit discriminates between the desired frequency signal andimage frequency signal. Further, a signal produced at the imagefrequency by each FET has a phase shift characteristic which changes inaccordance with changes in phase of the input signal. The output signalsproduced when the signal at the image frequency is down-converted to theIF frequency likewise have phase shifts which change in accordance withthe desired IF signal. Therefore, a signal produced at the imagefrequency, by the mixer circuit, will propagate toward the same outputterminal as the desired signal, thereby reducing the conversion loss ofthe mixer circuit.

In accordance with a further aspect of the present invention, the phaseand amplitude characteristics of output signals fed to the first andsecond outputs are tailored, such that, at a first output terminal theoutput signals combine in-phase, and at a second output terminal thesignals are out-of-phase such that a null or attenuated signal isprovided. Signals are fed to the output terminals in accordance with thefrequency of the input signal relative to the frequency of the localoscillator, over a wide bandwidth of input and intermediate signalfrequencies. In one embodiment, the amplitude tailoring is provided bycapacitively coupling a selected portion of the input signal to eachinput signal gate electrode. Phase shift tailoring is provided byselecting the phase shift characteristics of each one of the distributedinput signals fed to first input electrodes and distributed outputsignals fed from the output electrodes. With such an arrangement,amplitude tailoring and phase tailoring permit discrimination between aninput signal having a frequency either above or below the localoscillator signal over a wide band of input signal and intermediatesignal frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the inventionitself, may be more fully understood from the following detaileddescription of the drawings, in which:

FIG. 1 is a schematic diagram of a frequency conversion circuit, here amixer circuit;

FIG. 2 is a plan view of the circuit of FIG. 1 fabricated as a microwavemonolithic integrated circuit;

FIG. 3 is an exploded view of a portion of FIG. 2;

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3;

FIG. 5A is a simulated plot of input voltage signal distribution alongthe input coupling means;

FIG. 5B is a simulated plot of the input circuit relative phasedifferences between succeeding adjacent pairs of non-linear device:

FIG. 6 is a simulated plot of the magnitude of the transfercharacteristic of the circuit of FIG. 1 in accordance with the inputsignal profile of FIG. 5A and relative phase difference of FIG. 5B;

FIG. 7 is a typical noise spectrum produced by a local oscillatorfrequency signal;

FIG. 8 is a schematic diagram of an alternate embodiment of a frequencyconversion circuit, here a mixer circuit;

FIGS. 9-11 are schematic diagrams for alternate embodiments ofnon-linear elements for use with the circuits described in conjunctionwith FIGS. 1 and 8;

FIG. 12 is a schematic diagram of a further alternate embodiment of afrequency conversion circuit, here a frequency multiplier;

FIG. 13 is a schematic diagram of an alternate embodiment of anon-linear device for use in the invention as shown in FIG. 12;

FIG. 14 is a schematic diagram of a further alternate embodiment of afrequency conversion circuit; and

FIG. 15 is a schematic diagram for an alternate embodiment of thenon-linear elements for use with the circuit of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a frequency conversion circuit, here a mixercircuit 10 is shown to include a plurality of here four non-linearelements 15a-15d, each one having input electrodes 15a₁ -15d₁, 15a₂-15d₂ and output electrodes 15a₃ -15d₃. Here each non-linear element15a-15d includes a dual-gate field effect transistor FET 1-FET 4, biasedto operate as a non-linear device, for example FET 1-FET 4, may bebiased to operate as a half wave vth law device such as a half wavesquare law device. Each FET 1-FET 4 is successively coupled between aninput terminal 13, and a pair of output terminals 19a, 19b, and havefirst gate electrodes G_(1a) -G_(4a), second gate electrodes G_(1b)--G_(4b), drain electrodes D₁ -D₄ connected to respective electrodes ofnon-linear elements 15a-15d,respectively, as shown, and sourceelectrodes S₁ -S₄. A transmission line T₁, here a microstriptransmission line, is coupled at a first end to the input terminal 13via a d.c. blocking capacitor C₁ and a second end to an RF signal source11. First gate electrodes G_(1a) -G_(4a) are shown successivelyinterconnected together by input coupling means 16, here a travelingwave structure comprising a plurality of two port phase shift elementssuch as an artificial line or a distributed line. Here the two portelements comprise a plurality of distributed transmission lines T₂ -T₅,here each distributed transmission line T₂ -T₅ being a microstriptransmission line. Transmission line T₅ is coupled at a first end totransmission line T₄ and at a second end to a gate line terminationmatching network 22. Transmission line T₁ is fed an input signal(V_(rf)) which propagates along transmission lines T₁ -T₅. Selectedportions V_(rf1) -V_(rf4) of input signal V_(rf) are coupled torespective gate electrodes G_(1a) -G_(4a) preferably through a pluralityof coupling capacitors C₂ -C₅. Each transmission line T₂ -T₅ has aselected impedance and length to provide in combination with couplingcapacitors C₂ -C₅ a predetermined phase shift with respect to signalV_(rf) to each signal portion V_(rf1) -V_(rf4) of the input signalV_(rf). The coupling capacitors C₂ -C₅ in addition to contributing tothe phase shift characteristics imparted to the signals V_(rf1) -V_(rf4)also provide in combination with the intrinsic capacitance (not shown)between gates G_(1a) -G_(4a) and source electrodes S₁ -S₄ input signalshaving predetermined amplitudes. Suffice it here to say that theimpedance and length of transmission lines T₂ -T₅ and capacitance ofcoupling capacitors C₂ -C₅ are selected to provide predetermined phaseand amplitude relationships to input signals V_(rf1) -V_(rf4).

Second gate electrodes G_(2a) -G_(2d) are each fed a second inputsignal, here an in-phase equal amplitude signal from a common signalsource V_(L). Signal source V_(L) feeds an input terminal 18a to a powerdivider circuit 18 which provides four equal amplitude in-phase signalsV_(LO) (herein referred to as a local oscillator signal) at ports18b-18e.

Drain electrodes D₁ -D₄ are successively interconnected together by asecond, here output or drain coupling means 17, here a traveling wavestructure with said output coupling means 17 comprising a plurality oftwo port phase shifting elements such as an artificial line or aplurality of distributed transmission lines T₇ -T₁₁ and a plurality ofcapacitors C₈ -C₁₀, as shown. The transmission lines T₈ -T₁₀ are heremutually coupled microstrip transmission lines. The mutual coupling ofthe transmission lines T₈ -T₁₀, and capacitors C₈ -C₁₀ here provide thephase shifting elements having electrical pathlengths to provide therequisite phase shift at the frequency of the IF signals. Alternatively,artificial lines comprising a plurality of lumped inductors andcapacitors may be used. The particular choice of construction for thephase shift elements for either coupling means 16 or 17 is determined inaccordance with the frequency characteristic of signals which propagatethrough such coupling means 16, 17.

The mixer circuit 10 is shown to further include the gate linetermination network 22 coupled to transmission line T₅, including aresistor R₁, capacitor C₆, and a transmission line T₆, as shown. Adirect current path (DC path) to couple a gate bias source V_(GG) togates G_(1a) -G_(1d) is provided through resistors R_(G1) -R_(G4), asshown. Drain bias is here provided by an external biasing arrangement(not shown).

In operation, input signal portion V_(rf1) is coupled to gate electrodeG_(1a) through coupling capacitor C₂. As previously mentioned, capacitorC₂ has a capacitance selected in accordance with the inherent orintrinsic capacitance (not shown) of FET 1 to provide a voltage dividerand hence to provide a selected amplitude to signal V_(rf1). Succeedingportions V_(rf2) -V_(rf4) of the input signal V_(rf) are coupled to gateelectrodes G_(2a) -G_(4a) through coupling capacitors C₃ -C₅. In asimilar manner, capacitors C₃ -C₅ each have a capacitance selected inaccordance with the intrinsic gate-source capacitance of FET 2-FET 4,respectively, to provide signals coupled to said gate electrodes havinga selected or tailored amplitude. Each one of said signals V_(rf1)-V_(rf4) has a predetermined electrical phase shift related to thenumber of transmission line sections through which the signal propagatesbeyond transmission line T₂, as well as, the capacitance of therespective coupling capacitors.

Local oscillator signals V'_(LO) here of equal amplitude and equal phaseare fed to the second gate electrodes G_(1b) -G_(4b) and in combinationwith signals V_(rf1) -V_(rf4) produce output signals V_(IF1) -V_(IF4) atdrain electrodes D₁ -D₄. The output signals V_(IF1) -V_(IF4) eachinclude frequency components corresponding to the sum frequency (ω_(rf)+ω_(LO)), the difference frequency |ω_(RF) -ω_(LO) |, as well as, thefrequencies of the original signals ω_(rf), ω_(LO), harmonics of theinput signal Nω_(rf) and the local oscillator signal Mω_(LO), as wellas, intermodulation products of the components (Nω_(rf) ±Mω_(LO)). Herethe output coupling means comprising transmission lines T₇ -T₁₁ hascharacteristics selected to support propagation of the differencefrequency signal |ω_(rf) -ω_(LO) |, and preferably, filters or blocksthe frequency components of the RF signal, the local oscillator signal,the sum frequency component, the intermodulation products, the harmonicsof the local oscillator frequency signal, and the harmonics of the radiofrequency signal.

For the case where the input signal V_(rf) has a frequency ω_(rf) lessthan the frequency ω_(LO) of the local oscillator signal, at a first oneof the pair of terminals 19a, 19b, here terminal 19a, will be providedthe intermediate frequency signal having a frequency corresponding toω_(IF) =ω_(LO) -ω_(rf), with the second one of said pair of terminals19a, 19b, here terminal 19b providing a null or attenuated signal. Forthe second case, where the frequency of input signal ω_(RF) is greaterthan the frequency ω_(LO) of the local oscillator signal, at the secondoutput terminal terminal 19_(b) will be provided an intermediatefrequency signal having a frequency corresponding to ω_(IF) =ω_(rf)-ω_(LO) and at terminal 19a will be provided a null or attenuatedsignal. With this arrangement, the radio frequency mixer discriminatesbetween radio frequency signals having a frequency either above or belowthat of the local oscillator signal. That is, the mixer discriminatesbetween the desired signal and the image signal. The followingdiscussion and accompanying Table 1 are useful in understanding how themixer circuit 10 discriminates between the desired IF signal and imageIF signal.

                                      TABLE I                                     __________________________________________________________________________    ω.sub.rf > ω.sub.LO                                                                         ω.sub.rf < ω.sub.LO                     FET                                                                              ω.sub.rf                                                                      phase shift                                                                         IF freq.                                                                           phase shift                                                                         ω.sub.rf                                                                      phase shift                                                                         IF freq.                                                                           phase shift                        __________________________________________________________________________    1  ω.sub.LO + ω.sub.IF                                                     0     ω.sub.IF                                                                     0     ω.sub.LO - ω.sub.if                                                     0     ω.sub.IF                                                                      0                                 2  ω.sub.LO + ω.sub.IF                                                     θ                                                                             ω.sub.IF                                                                     θ                                                                             ω.sub.LO - ω.sub.if                                                     θ                                                                             ω.sub.IF                                                                     -θ                           3  ω.sub.LO + ω.sub.IF                                                     2θ                                                                            ω.sub.IF                                                                     2θ                                                                            ω.sub.LO - ω.sub.if                                                     2θ                                                                            ω.sub.IF                                                                     -2θ                          4  ω.sub.LO + ω.sub.IF                                                     3θ                                                                            ω.sub.IF                                                                     3θ                                                                            ω.sub.LO - ω.sub.if                                                     3θ                                                                            ω .sub.IF                                                                    -3θ                          __________________________________________________________________________

As an illustrative example, consider the case where each one of lines T₃-T₅ and T₈ -T₁₀ provide phase shifts of θ_(rf) and θ_(IF), respectively,where θ_(rf) and θ_(IF) are the same phase shift equal to 90° at therespective rf and IF frequencies where this condition is satisfied,where the phase shift contribution of the FETS, as well as, thecapacitors can be ignored, and where C₂ =C₃ =C₄ =C₅ =∞.

Over a narrow frequency band, for ω_(rf) <ω_(LO), signals V_(1a) -V_(4a)will substantially add in-phase at terminal 19a and will providesubstantially a null or attenuated signal at terminal 19b. Similarly,over a narrow band where ω_(rf) >ω_(LO), signals V_(1b) -V_(4b) will addin-phase at terminal 19b and will provide a null or attenuated signal atterminal 19a.

This may be demonstrated as follows: V_(rf1) has a relative phase shiftof 0° with respect to itself and thus V_(IF1) similarly has a relativephase shift of 0°. Thus, signal component V_(IF1a) has a phase shift of0° at terminal 19a, whereas signal component V_(IF1b) has a phase shiftof 3θ_(IF) at terminal 19b. The intermediate signal V_(IF2) has a phaseshift relative to V_(IF1) corresponding to θ_(rf). Signal componentV_(IF2a) which propagates toward terminal 19a has a composite phaseshift of θ_(rf) +θ_(IF) =2θ and the signal component V_(IF2b) whichpropagates toward terminal 19b has a composite phase shift of θ_(rf)+2θ_(IF) =3θ. Thus, at terminal 19a signal component V_(IF2a) incombination with the signal component V_(IF1a) provides a null orstrongly attenuated signal since components V_(IFla), V_(IF2a) aresubstantially of equal magnitude and 180° out-of-phase (as assumedθ=90°). The second signal component V_(2b) combines in-phase at terminal19b with signal V_(IF1b). Similarly, the intermediate signal V_(IF3) hasa phase of 2θ_(rf). Signal component V_(IF3a) propagates toward terminal19a having a composite phase shift of 2θ_(rf) +2θ_(IF) =2π+0° and signalcomponent V_(IF3b) propagates toward terminal 19b having a compositephase shift of 2θ_(rf) +θ_(IF) =3θ. Signal V_(IF3b) combines in-phase atterminal 19b with the signals V_(IF1b), V_(IF2b). The fourth signalV_(4IF) has a phase shift of 3θ_(rf). Signal component V_(IF4a)propagates towards terminal 19a having a composite phase shift of3θ_(rf) +3θ_(IF) =2π+2θ and signal component VIF4b propagates towardterminal 19b having a composite phase shift of 3θ_(rf). Signal V_(IF4a)arrives at terminal 19a having a phase shift equivalent to 2θ thusout-of-phase with signal component V_(IF3a). Thus, a null signal isprovided at terminal 19a. On the other hand, signal V_(IF4b) arrives atterminal 19b having a relative phase shift of 3θ_(IF) or 3θ andtherefore adds in-phase at terminal 19b with the signals V_(IF3b),V_(IF2b) and V_(IF1b) previously coupled to terminal 19b. Accordingly,it is now clear that by selecting the phase shifts between inputsignals, and the IF output signals from adjacent pairs of transistors(i.e., FET 1, FET 2 and FET 3, FET 4) the IF signals will beout-of-phase at terminal 19a, but will be in-phase at terminal 19b.

For the case where ω_(LO) >ω_(rf), the difference frequency signal(ω_(LO) -ω_(rf)) will provide a signal at terminal 19a signal having thefrequency ω_(IF) =ω_(LO) -ω_(rf) and a null or strongly attenuatedsignal at terminal 19b. This can be seen by a similar analysis asdescribed above. From each drain electrode a signal will propagate ineach of two directions toward terminals 19a, 19b. However, the initialphase shifts from signals V_(IF1) -V_(IF4) which couple from drainelectrodes D₁ -D₄ will have a phase lag rather than phase lead, as alsoshown in Table I, that is, will have a negative phase shift. Therefore,the phases of the signals coupled from each one of the drain electrodesD₁ -D₄ will couple to output terminal 19a having a relative phase shiftof 0° and will couple to terminal 19b having relative phase shifts of -θor +θ. Therefore, at terminal 19a will be provided the intermediatefrequency signal ω_(IF) equal to (ω_(LO) -ω_(rf)) and at terminal 19bwill be provided the null or strongly attenuated signal.

Preferably, however, the capacitors C₂ -C₅, rather than being equal, asassumed above, are selected in accordance with the inherent capacitance(not shown) between the first gate and source of each FET to provideselected input signal amplitude tailoring to the signals fed to eachfirst gate electrode G_(1a) -G_(4a). The transmission lines T₃ -T₅and/or T₇ -T₉ have selected impedances and electrical pathlengths, asdescribed above to provide selected phase shift tailoring. With thisarrangement, capacitors C₂ -C₅ are here used to tailor the input voltageto each FET as a function of frequency. Further, the capacitors C₂ -C₅and transmission lines T₃ -T₅, T₇ -T₉ provide tailored electricalpathlengths to signals V_(rf1) -V_(rf4) or V_(IF1) -V_(IF2) in order toprovide the high directivity of propagation of IF signal componentsVla-V4a toward terminal 19a and V_(1b) -V_(4b) toward terminal 19b overa wide bandwidth.

Referring now to FIGS. 2-4, the mixer 10 (FIG. 1) is shown fabricated asa monolithic integrated circuit 10'. The mixer 10' is formed on asubstrate 40, here comprised of gallium arsenide or other suitable GroupIII-V material or other semiconductor material. The substrate 40 hasformed on a bottom surface portion thereof, a ground plane conductor andon an upper surface portion thereof, a mesa-shaped epitaxial layer 44(FIGS. 3, 4). The mesa-shaped layer 44 provides active regions for fieldeffect transistors FET 1-FET 4. Here, each FET is identical inconstruction and includes a pair of source electrodes and a common drainelectrode spaced by one gate electrode of each of a pair of gateelectrodes (not numbered), as shown. Thus considering an exemplary oneof such field effect transistors, here FET 4, such transistor is shownin FIGS. 3 and 4 to have a common drain pad D₄ connected by stripconductors T_(s10), T_(s11) and a pair of source contacts S_(4a), S_(4b)connected to ground plane conductor 42 through plated via holes 47 (FIG.2). FET 4 is shown to further include a gate pad G_(4a) having connectedthereto a pair of gate fingers G_(4a1), G_(4a2) and a second gate padregion G_(4b) having a second pair of gate fingers G_(4b1), G_(4b2).Source electrodes S_(4a) and S_(4b) are spaced from drain electrode D₄by one gate finger of each pair G_(4a1), G_(4a2) and G_(4b1), G_(4b2) ofgate fingers. A conductor 45 is formed on the substrate 40 to feed thegate bias signal from gate bias source (not shown) to each one of thegate electrodes. The conductor 45 is coupled to each one of the gateelectrodes through resistors R_(G1) -R_(G4), as shown. Here resistorsR_(G1) -R_(G4) are provided by open or floating gate MESFETS, as shownin FIGS. 3 and 4 for resistor R_(G4). Resistors R_(G1) -R_(G4) eachprovide a relatively high resistance approximately equal to 2K ohms. Thedrain and source electrodes D, S provide the ohmic contact terminals forresistor R_(G4). Coupling capacitor C5, as shown in FIGS. 3, 4, includesa first electrode C_(5a) disposed on the semi-insulating substrate 40, adielectric C_(5b) disposed over the first electrode C_(5a), and a secondelectrode contact C_(5c) disposed over a portion of the dielectricC_(5b). The second electrode contact C_(5c) is directly connected tostrip conductor T_(s5) and resistor R₁, here a metal film resistor. Thebottom contact C_(5a) of capacitor C₅ is connected to gate electrodefingers G_(4a1) and G_(4a2). The bottom contact C_(5a) is connected tothe aforesaid mentioned gate contact G_(4a) of field effect transistorFET 4. Thus, an input signal propagating along transmission lines T₂ -T₆is coupled to gate electrodes G_(4a1), G_(4a2) through capacitor C₅,whereas, the bias signal provided from resistor R_(G1) is coupleddirectly to gate electrode fingers G_(4a1), G_(4a2). A similararrangement is provided with field effect transistor FET 1. The gateelectrodes G_(2a), G_(3a) of field effect transistors FET 2 and FET 3are here connected directly to the transmission line sections T₂, T₃ andT₄.

As further shown in FIG. 2, the strip conductors T_(s8) -T_(s10) arearranged to provide a mutually coupled line, that is, the stripconductor is arranged in a coiled fashion having upper portions bridgingover underlying portions of the strip conductors T_(s8) -T_(s10).Capacitors C₈ -C₁₀ are shunted to ground by interconnections to sourcepads, as shown. The width of the strip conductors, the gap between stripconductors and the length of the strip conductors are chosen for eachone of said strip conductors T_(s8) -T_(s10) to provide a predeterminedelectrical pathlength at the intermediate frequency signal of the mixer,as shown for example in Table 2. Here mutually coupled transmission linesections T₈ -T₁₀ and capacitors C₈ -C₁₀ are provided to selectivelyincrease the electrical pathlength of each one of the transmission linesover the corresponding frequency bandwidth of the intermediate frequencysignals, here 2 to 8 GHz. With this arrangement, the output couplingmeans comprises substantially distributed transmission line sections,whereas, the relatively large electrical pathlengths required for thedistributed transmission lines between each one of the field effecttransistors is provided, in part, by the mutual coupling between thelines, as well as, the capacitors C₈ -C₁₀ shunted to ground.

A mixer 10, as described in FIGS. 1-4, was designed the followingcharacteristics: The circuit was modeled to be fabricated on a 4 milthick GaAs substrate having disposed thereon four dual gate MESFETs,each MESFET having a 200 μm gate periphery. The mixer was designed tooperate over an input signal bandwidth of 14 GHz to 20 GHz, IF bandwidth2 Ghz to 8 Ghz at a local oscillator frequency of 12 GHz. All componentvalues given below in Table 2 are modeled at 17 Ghz for input circuitcomponents and 5 GHz for output circuit components. The phase shift ofinput transmission lines includes the phase shift provided by capacitorsC₂ and C₅, and is measured with respect to the phase of the signalV_(1rf) at the gate electrode G_(1a).

                  TABLE 2                                                         ______________________________________                                        Transmission Lines      Capacitors                                            Width of     Electrical                                                       Strip Conductors                                                                           Pathlength     Capacitance                                       ______________________________________                                        Input circuit                                                                 T.sub.3                                                                              .049 mm   θ.sub.3 = 55°                                                                   C.sub.2 = 0.15 pf                             T.sub.4                                                                              .036 mm   θ.sub.4 = 61°                                                                   C.sub.3 = α                             T.sub.5                                                                              .026 mm   θ.sub.5 = 59°                                                                   C.sub.4 = α                                                             C.sub.5 = 0.37 pf                             Output circuit                                                                       (W)       (G)        (L)                                                      width     gap        length                                            T.sub.7                                                                              .025 mm   .028 mm    1.2 mm                                                                              C.sub.8 = 0.5 pf                            T.sub.8                                                                              .025 mm   .018 mm    1.0 mm                                                                              C.sub.9 = 0.5 pf                            T.sub.9                                                                              .025 mm   .028 mm    1.2 mm                                                                              C.sub.10 = 0.5 pf                           ______________________________________                                    

Referring to FIGS. 5A, 5B and 6, the input voltage profile at each FETas a function of frequency (FIG. 5A), the relative differential phaseshift between succeeding adjacent pairs of input electrodes as afunction of frequency (FIG. 5B), and the IF frequency output response(FIG. 6) at terminals 19a, 19b (FIG. 1) are shown, respectively, for thecircuit designed in accordance with the parameters of Table 2. FIG. 5Ashows the general shape of the input voltage amplitude distributionchosen to provide the relatively flat, desired output response (FIG. 6)at the IF frequency at terminal 19b and provides a null or attenuatedresponse at terminal 19a. The attenuated input excitations to FET 1 andFET 4 are here provided by coupling capacitors C₂ and C₅, respectively.Furthermore, the varied transmission line capacitance also contributesto the general shape of the voltage distribution at each FET. Here theinput coupling means 16 was optimized to provide the desired flat outputresponse (FIG. 6) at terminal 19b (curve 68) and a null or attenuatedsignal at terminal 19b (curve 70) in response to r.f. input signalshaving a frequency greater than that of the local oscillator. However,given a desired output response at terminal 19a for input signals havinga frequency less than that of the local oscillator, the input circuitcould be re-optimized, as will now become apparent to those skilled inthe art, by changing the values of capacitors C₂ -C₅, capacitances oflines T₂ -T₅ and electrical pathlengths of lines T₂ -T₅. Moreover, theinput coupling means may be further re-optimized to provide an outputsignal response at a first one of terminals 19a, 19b and a null orattenuated response at the second one of terminals 19a, 19b inaccordance with the frequency of the input signal as described above.

As shown in FIG. 5B, the differential phase (expressed as a phase lag)between the first gate electrodes G_(1a) -G_(4a) of successive adjacentpairs of FETS (FET 2 and FET 1, curve 62, FET 3 and FET 2, curve 64, FET4 and FET 3, curve 66) was selected to be approximately 90° at themidband frequency (here 17 GHz). However, even though the phase shiftchanged to 70° at 14 GHz and to about 115° between FET 2 and FET 3 at 20GHz, the output response (FIG. 6) still shows relatively gooddirectivity of the IF signal produced by the desired input signal at theextremes (2 and 8 GHz) of the IF frequency band.

Preferably, the impedance of transmission lines T₂ -T₅ is also selectedin accordance with capacitors C₂ -C₅, and the intrinsic capacitance (notshown) between the gate electrodes G_(1a) -G_(4a) and source electrodesS₁ -S₄ to provide the mixer 10 with a predetermined input impedance,preferably related to the impedance of transmission line T₁. In asimilar manner, the characteristic impedance of transmission lines T₈-T₁₀ is selected in accordance with the intrinsic capacitance (notshown) between drain electrodes D₁ -D₄ and source electrodes S₁ -S₄,respectively, to provide the mixer 10 with a predetermined outputimpedance. Such an arrangement to provide selected input and outputimpedances is described in U.S. Pat. No. 4,456,888 issued June 26, 1984,and assigned to the same assignee as the present invention.

The field effect transistor when biased as a non-linear device generatesspurious or undesirable frequency components, one of which is the secondharmonic of the local oscillator signal. The mixing of the secondharmonic of the LO and the input signal (ω_(rf) -2ω_(LO)) produces asignal at the image frequency ω_(IM). This signal is particularlyundesirable because the signal produced at the image band frequencyincreases the conversion loss of the mixer. However, with the abovearrangement, because the phase of the input signal changes at each fieldeffect transistor in accordance with the propagation of the input signalthrough transmission lines T₂ -T₅ and the IF signals throughtransmission lines T₈ -T₁₀, the phase of the image signal created bymixing the second harmonic of the LO and the input signal also changesas does the phase of the IF frequency when the signal produced at theimage frequency is down-converted to the IF frequency. The phases of theimage rf and IF signals are shown in Table 3 below. The direction of thephase progression indicates that the signal produced at the imagefrequency will propagate back in the direction of the signal source.Along this propagation, some of this signal is fed back to FET 1-FET 4and down-converted to the IF image frequency. The resulting IF imagesignal will propagate in the same direction as the desired IF signalprovided in response to the input signal, and therefore, the signalproduced at the image frequency will be provided at the same terminal asthe desired IF signal. This will reduce conversion loss of the mixercircuit.

                  TABLE 3                                                         ______________________________________                                        ω.sub.rf > ω.sub.LO                                                              Image signal  IF from Image                                                   phase           phase       phase                              FET  rf        shift   freq.   shift freq. shift                              ______________________________________                                        1    ω.sub.LO + ω.sub.IF                                                         0       ω.sub.LO - ω.sub.IF                                                       0     ω.sub.IF                                                                      0                                  2    ω.sub.LO + ω.sub.IF                                                         θ ω.sub.LO - ω.sub.IF                                                       θ                                                                             ω.sub.IF                                                                      θ                            3    ω.sub.LO + ω.sub.IF                                                         2θ                                                                              ω.sub.LO - ω.sub.IF                                                       2θ                                                                            ω.sub.IF                                                                      2θ                           4    ω.sub.LO + ω.sub.IF                                                         3θ                                                                              ω.sub.LO - ω.sub.IF                                                       3θ                                                                            ω.sub.IF                                                                      3θ                           ______________________________________                                    

The mixer circuit 10 (FIG. 1) also provides substantially completecancellation of noise introduced into the IF band by the localoscillator signal. As seen in FIG. 7, noise associated with the localoscillator frequency signal is in general clustered in a relativelynarrow band about the local oscillator frequency f_(LO). However, whilethis condition is not a prerequisite for noise cancellation to occur inthe circuit described in FIG. 1, assumption of this condition makes thefollowing analysis easier.

For noise cancellation to occur in the circuit of FIG. 1, it isgenerally required that the local oscillator frequency excitation ofeach field effect transistors FET 1-FET 4 be in-phase and of equalamplitude. Each frequency component of the noise, therefore, will mixwith the local oscillator carrier frequency and be down-converted to theIF band. This includes noise in both the upper and lower side bands ofthe local oscillator signal. The phase difference between the noisecomponents of the IF ports, IF₁ and IF₂, will be substantially equal tozero since the local oscillator excitation of each field effecttransistor FET 1-FET 4 arises from input signals provided from the samesignal source having substantially equal phase and amplitude.

Assuming that the IF noise voltage component at the nth IF port isdenoted by e_(n) (f_(m)) where f_(m) is the frequency offset of thenoise component from the carrier such as shown in FIG. 8, and, n is thenumber of IF ports (not necessarily equal to four), then because alle_(n) signals are from the same local oscillator frequency source, thesecomponents are fully correlated and can be added algebraically. Takingthe phase shift introduced between the IF ports by the IF circuit intoconsideration, the noise voltage corresponding to the frequencycomponent f_(m) at the two IF ports labeled 19a and 19b in FIG. 1 isgiven by: ##EQU1## For balanced mixers, e.sub. =e_(k) for all n and k.Thus, ##EQU2## Therefore, for all other frequency components about thelocal oscillator carrier frequency, the above relationship is true. Itis evident that complete noise cancellation of the frequency noiseoccurs when θ is chosen to satisfy the condition θ=2π/N for (N>1).

For example, for four field effect transistors, as shown in FIG. 1, N=4,the required phase shift between field effect transistor and IFterminals is 90°. This simple case may be shown by a vector diagram (notshown) of the noise voltage components at each IF port. Because of the90° phase shift, the components are added vectorially as the four-sidesof a square to a null vector.

Referring now to FIG. 8, an alternate embodiment of a frequencyconversion circuit, here a mixer circuit 60 is shown. Mixer circuit 60includes the aforementioned output coupling means 17, input couplingmeans 16, and a plurality of non-linear elements 15a-15d, here eachincluding the field effect transistors FET 1-FET 4 as described inconjunction with FIG. 1. Mixer circuit 60 is shown to further include asecond input traveling wave structure 62, here comprising a plurality ofdistributed transmission lines T₁₂ -T₁₆, here each one of saidtransmission lines being a microstrip transmission line. A first end oftransmission line T₁₆ is terminated in a characteristic impedance, hereshown as R₂, and a first end of said distributed transmission line T₁₂is coupled to a local oscillator signal V_(LO). Accordingly, localoscillator signal V_(LO) propagates along transmission line sections T₁₂-T₁₆, with portions of said signals V_(LO) '₁ -V_(L0) '₄ being fed fromsaid transmission lines to each one of the corresponding gate electrodesG_(1b) -G_(4b). The local oscillator signal is fed to terminal 18a' andpropagates along transmission mission lines T₁₄ -T₁₆ havingprogressively or successively increasing phase shifts. As before, theinput signal V_(rf) propagates along transmission lines T₂ -T₅ and iscoupled to corresponding gate electrodes G_(1a) -G_(4a). Since the localoscillator V_(LO) and the input signal V_(rf) propagate in oppositedirections, the relative phase shift difference between the pair ofsignals will be the sum of the respective phase shifts at the inputelectrodes of each one of the field effect transistors. Accordingly, thepathlength of the traveling wave structure 62 for the local oscillatorsignal may be adjusted to provide additional control of the phase shiftof the signals coupled to the output or drain electrodes of each one ofthe field effect transistors. Accordingly, the phase shift of the IFsignal at the output of each one of the field effect transistors becomesthe sum of the phase shift from the r.f. input signal line, and thephase shift from the local oscillator signal line. Preferably, as shownin FIG. 7, coupling capacitors C₂ -C₅ are used to provide amplitudetailoring to the input signals as described in conjunction with FIG. 1.Further, by providing a traveling wave structure 62 to feed the localoscillator signal to each FET, the local oscillator signal may be sweptor varied over a broad range of frequencies.

Referring now to FIGS. 9-11, alternate embodiments for the mixerelements 15a-15d (FIG. 1) are shown. As an illustrative example, element15a is shown in FIG. 9 having dual-gate field effect transistor FET 1(FIG. 1) replaced by a diode D₁ and a capacitor C coupled in shuntbetween a cathode of diode D₁ and ground. The local oscillator signalV_(LO) and the radio frequency input signal (V_(rf)) are fed viaterminal 15_(a1) to an anode of diode Dl with the cathode providing theoutput signal V_(IF1) at terminal 15_(a3). Similarly, as shown in FIG.10, the dual-gate field effect transistor FET 1 (FIG. 1) may be replacedby a single gate field effect transistor, here FET 1', having a firstone of drain and source electrodes D', S' being fed via terminal 15_(a1)by an RF signal (V_(rf)) and the gate electrode, for example, being fedvia terminal 15_(a2) by the local oscillator signal (V_(LO)) with thesecond one of the drain and source electrodes providing the outputsignal V_(IFl) at terminal 15a₃. Similarly, as shown in FIG. 11,dual-gate field effect transistor FET 1 (FIG. 1) may be replaced by apair of field effect transistors FET 2', FET 3'. The first field effecttransistor FET 2' connected in a common source configuration has a gateelectrode G₂ ' fed, via terminal 15a₁, the r.f. input signal V_(rf) andprovides an output signal to a first one of drain and source electrodesD₃ ', S₃ ' of the field effect transistor FET 3'. The field effecttransistor FET 3' is fed, via terminal 15a₂, the local oscillator signal(V_(LO)) which modulates the transconductance of field effect transistorFET 3' to produce the mixed output signal V_(IFl) at terminal 15a₃. Itcan be seen, therefore, by substituting the dual-gate field effecttransistors FET 1-FET 4 of FIG. 1 with any one of the above devicesbetween the input coupling means 16 and output coupling means 17,alternate embodiments of the frequency conversion circuit may beprovided.

Referring now to FIG. 12, a further alternate embodiment of a frequencyconversion circuit, here a distributed frequency multiplier 80 is shownto include a first plurality or set of here four field effecttransistors FET 11-FET 14 successively coupled between an input terminal82 and an output terminal 83, via a plurality of two port phase shiftelements such as an artificial line or a distributed line. Here againnon-linear elements are provided with element 15a only shown forclarity. Here the two port elements comprise a plurality of distributedinput transmission lines T₂₁ -T₂₅ and a plurality of output transmissionlines T₂₆ -T₂₉ and T₃₀ -T₃₄. Here transmission lines T₂₁ -T₃₄ aremicrostrip transmission lines. The field effect transistors FET 11 toFET 14 have input electrodes, here gate electrodes G₁₁ to G₁₄,respectively, successively electrically interconnected via the firstplurality of transmission lines T₂₁ -T₂₅. The output electrodes, heredrain electrodes D₁₁ -D₁₄ are successively electrically interconnectedvia transmission lines T₂₆ -T₂₉ and common output lines T₃₀ -T₃₄. Sourceelectrodes S₁₁ to S₁₄ of transistors FET 11 to FET 14, respectively, areconnected to a reference potential, here ground, through a common RF andDC path, as shown. The gate electrode of the first one of the fieldeffect transistors, here gate electrode G₁₁ of FET 11 is coupled toinput terminal 82 through transmission line T₂₁, whereas the drainelectrode D₁₁ of the first field effect transistor FET 11 is coupled toan RF output terminal 83 through transmission lines T₂₆ and T₃₀. Asucceeding one of the field effect transistors, here the last or fourthfield effect transistor FET 14 has an input or gate electrode G₁₄coupled to a gate DC bias circuit 92 through transmission line T₂₅, asshown, and has the output or drain electrode D₄ of such field effecttransistor FET 4 coupled via transmission lines T₂₉ and T₃₄ to theoutput or drain bias circuit 90, as shown.

The distributed frequency multiplier circuit 80 is shown to furtherinclude a second plurality of here four field effect transistors FET15-FET 18 successively coupled between an input terminal 82' and theoutput terminal 83 via a second plurality of two port phase shiftelements such as an artificial line or a distributed line. Here againnon-linear elements are provided as shown in FIGS. 1, 8 and as shown forFET 11, as described above. Here the two port elements comprise aplurality of distributed input transmission lines T₂₁ ' to T₂₅ ', and asecond plurality of two port elements or drain transmission lines T₂₆ 'to T₂₉ ' and the common output drain transmission lines T₃₀ to T₃₄. Thefield effect transistors FET 15-FET 18 have input electrodes, here gateelectrodes G₁₅ -G₁₈, respectively, successively electricallyinterconnected via the second plurality of transmission lines T₂₁ ' toT₂₅ ', here each line being a microstrip transmission line. The outputelectrodes, here drain electrodes D₁₅ -D₁₈ of field effect transistorsFET 15-FET 18, respectively, are successively electricallyinterconnected via the drain electrode transmission lines T₂₆ ' to T₂₉ 'and the common transmission lines T₃₀ ', T₃₄ '. The source electrodesS₁₅ -S₁₈ of transistors FET 15-FET 18, respectively, are connected to areference potential, here ground, through a common DC and RF path, asshown. The gate electrode of the first one of the second set of fieldeffect transistors, here gate electrode G₁₅ of FET 15 is coupled to theinput terminal 82', via transmission line T₂₁ ', whereas the drainelectrode D₁₅ of the first field effect transistor FET 15 of the secondset of field effect transistors is coupled to the output terminal 83 viatransmission line T₂₆ ' and T₃₀. A succeeding one of the field effecttransistors, here the last or fourth field effect transistor, here FET18 of the second set of field effect transistors has an input or gateelectrode G₁₈ coupled to a gate DC bias circuit 92' via transmissionline T₂₅ ', as shown, and the output or the drain electrode D₁₈ of suchfield effect transistor FET 18 is coupled to the output or drain biascircuit 90 via transmission lines T₂₉ ' and T₃₄, as shown.

The drain bias circuit 90 is here a ladder network having three shuntpaths to ground via capacitors C₁₃, C₁₄, C₁₅ with transmission lines,here microstrip transmission lines T₃₆, T₃₇ and T₃₈ providing serialelements of such network. A pair of bias terminals 91a, 91b are adaptedfor coupling to a grounded DC bias source V_(DD), such terminal 21abeing connected to capacitor C₁₅ and transmission line section T₃₈, asshown. Capacitors C₁₃, C₁₄ and C₁₅ provide a relatively low impedancepath to radio frequency (RF) signals and thus shunt such radio frequencysignals to ground to prevent such RF signals from being coupled to theDC bias source V_(DD). A resistor R₁₂ is shown coupled in shunt withground and the connection between transmission line T₃₆ and transmissionline section T₃₄. Resistor R₂ in combination with the compositeimpedance of transmission line sections T₃₆, T₃₇ and T₃₈ and capacitorsC₁₃, C₁₄ and C₁₅ provide a complex impedance for matched termination oftransmission line section T₃₄.

Gate bias circuits 92 and 92' are substantially identical and thereforethe description of gate bias circuit 92 is likewise applicable to gatebias circuit 92'. The gate bias circuit 92 is also a ladder network andincludes a serially connected resistor R₁₁ and transmission line sectionT₃₅. Transmission line section T₃₅ and resistor R₁₁ provide a directcurrent path between input bias terminal 26 and the microwavetransmission lines T₂₁ -T₂₅. Radio frequency bypass capacitors C₁₁ andC₁₂ are coupled in shunt between the ends of transmission line sectionT₃₅ and ground. Again, such radio frequency bypass capacitors C₁₁, C₁₂provide low impedance paths to radio frequency signals shunting suchradio frequency signals to ground and thereby isolate such radiofrequency signals from a voltage source V_(GG) which is coupled betweenground terminal 23b and terminal 23a.

The characteristics of drain and gate bias circuits are selected toplace each of the field effect transistors in the non-linear or squarelaw region of their respective transfer characteristics.

A signal is fed from a source V_(rf) to a directional coupler 86 whichprovides at its output terminals (not numbered) a pair of input signalsV_(S), V_(S) ' having a 180° differential phase shift. Alternatively,the input signal V_(rf) may be fed to a common junction including a pairof transmission lines having a differential pathlength corresponding toa phase shift of 180°. Thus, the first signal V_(S) is coupled to inputterminal 82 and propagates along transmission lines T₂₁ to T₂₅. Aportion of signal V_(S) is coupled to each one of the gate electrodesG₁₁ to G₁₄ of FET 11-FET 14. At the output of the corresponding drainelectrodes D₁₁ to D₁₄, an output signal appears having frequencycomponents equal to ω_(o), 2ω_(o), 3ω_(o), . . . nω_(o) where n is aninteger greater than 1 and ω_(o) is the fundamental frequency of theradio frequency input source V_(rf), and where 2ω_(o), 3ω_(o), . . .nω_(o) are the even and odd harmonics of the fundamental frequencyω_(o). Similarly, the second signal V_(S) ' is fed to the input terminal82' and such signal propagates along transmission lines T₂₁ ' to T₂₅ 'and a portion of such signal is coupled to gate electrodes G₁₅ to G₁₈.In response, an output signal is produced at each of the drainelectrodes D₁₅ to D₁₈, having frequency components ω_(o), 2ω_(o),3ω_(o), . . . nω_(o), again where n is equal to an integer greater than1 and ω_(o) is the fundamental frequency of the radio frequency sourceV_(rf). Signals from drain electrodes D₁₁ to D₁₄ and D₁₅ to D₁₈ arecoupled to radio frequency transmission lines T₃₀ -T₃₄ at correspondingjunctions 86a-86d. The same electrical pathlengths are provided betweeneach one of said input terminals 82, 82' and output terminal 83 throughrespective ones of each of said pairs of field effect transistors (i.e.,FET 11, FET 15; FET 12, FET 16; FET 13, FET 17; and FET 14, FET 18).Since the input signals V_(S), V_(S) ' are fed to terminals 82 and 82'having a 180° differential phase shift, signals coupled from respectivepairs of drain electrodes D₁₁ and D₁₅, D₁₂ and D₁₆, D₁₃ and D₁₇, D₁₄ andD₁₈ will have the fundamental frequency components having the 180°differential phase shift, and the odd harmonics of the fundamental willlikewise have a 180° differential phase shift. Therefore, the initialphase relationship of 180° provided by the coupler 30 is maintained ineach frequency component of the signal having an odd multiple harmonicrelationship with the fundamental. With this arrangement, all the oddharmonics (2n+1)ω_(o) of the fundamental frequency component of thesignal including the fundamental component coupled from the outputterminal 83 will cancel at terminal 83. On the other hand, since thedevices are half-wave vth, more preferably, square law, non-lineardevices, all the even harmonics (2n)ω_(o) will have a phase differencecorresponding to multiples of 0° and therefore all of the even harmonicswill be summed in-phase and will appear at the output terminal 83, as acomposite signal V_(O).

At the output terminal 83 the composite signal is provided having evenharmonic frequency components. A selected frequency component may berecovered from such signal in one of several ways. One approach is toprovide the output coupling lines T₂₆ -T₂₉, T₂₆ '-T₂₉ ' and T₃₀ -T₃₄with a bandpass filter characteristic permitting only the selected evenharmonic to propagate therethrough. An alternative way is to provide alumped filter arrangement at the output of the radio frequency terminal83 to pass the desired even harmonic.

Preferably, in order to provide relatively broadband performance, thatis, operation over a relatively broad range of input signal frequencies,the characteristic impedance of each one of the transmission lines T₂₁-T₂₅, T₂₁ '-T₂₅ ' is selected in accordance with the inherent inputreactance between gate and source of the field effect transistors FET11-FET 14 and FET 15-FET 18 to provide an input network having apredetermined characteristic impedance. In a similar manner, thecharacteristic impedance of the output transmission lines T₂₆ -T₂₉, T₂₆'-T₂₉ ' and T₃₀ -T₃₄ are selected in accordance with the inherent outputreactance between drain and source of such field effect transistors FET11-FET 14 and FET 15-FET 18 to provide an output network having apredetermined output impedance. Such an arrangement is described in theU.S. Pat. No. 4,456,888 issued June 26, 1984, and assigned to the sameassignee as the present invention.

Referring now to FIG. 13, an alternate embodiment for a non-lineardevice, here a diode such as Schottky diodes 96, 96', are shown. TheSchottky diode would be used to replace the field effect transistors(FET 11, FET 15) as illustratively shown in FIG. 13. The diode being anon-linear device would provide similar signal cancellation by properphasing of the odd harmonics of the output signals and signalenhancement of the even harmonics, as described above.

Referring now to FIG. 14, a further alternate embodiment of a frequencyconversion circuit, here a mixer 110, is shown to include the firstplurality of here four non-linear elements 15a-15d, here each one ofsaid elements including one of the active elements described inconjunction with FIGS. 9-11 or the dual-gate field effect transistorshown in FIG. 15. Here said non-linear elements are, for example, halfwave vth law devices, such as a half wave square law device. Each one ofsaid non-linear elements 15a-15d is coupled to a corresponding one of aplurality of output phase shifting elements 117a-117d. Each one of saidphase shifting elements 117a-117d includes respective pairs of anygeneralized two port elements 117a'-117d' and 117a"-117d", here each oneof said two port phase shifting elements may include an artificial lineor a distributed transmission line. Alternatively, the pairs of two portelements may be active devices such as an amplifier or othernon-reciprocal two port elements. Here one of said two port distributedlines has a common connection which is coupled to respective outputports 15a₃ -15d₃ of respective ones of the non-linear elements 15a-15dand has a pair of input ports connected to one of a pair of outputterminals 19a, 19b of the circuit. The circuit 110 is shown to furtherinclude an input coupling means 116, here comprising a plurality oftransmission lines 116a-116d, each one of said lines having apredetermined electrical pathlength, to provide a differentialpathlength or phase shift between adjacent successive pairs of saidlines 116a-116d. An input signal V_(rf) is fed to an input terminal 113of the circuit and said signal is distributed to each one of saidtransmission lines 116a-116d from a common connection with terminal 113.The outputs of said transmission lines 116a-116d are fed preferablythrough one of a corresponding plurality of capacitors C₁₂ -C₁₅ with theoutput of said capacitors feeding input terminals 15a₁ -15d₁ of therespective non-linear elements 15a-15d. A second input signal, here alocal oscillator signal, is coupled to a second input terminal 118a, andsaid signal is fed to a local oscillator coupling means 118. Localoscillator coupling means 118 here comprises a plurality of here four,two port phase shifting elements 118b-118e, here said elementscomprising a distributed transmission line. The phase shifts θ_(LO1)-θ_(LO4) provided by said distributed transmission lines 118b-118e in afirst embodiment of the local oscillator means 118 have substantiallyequal pathlengths and in a second embodiment of the means, theelectrical pathlengths θ_(LO1) -θ_(LO4) have successively increasingelectrical pathlengths. The outputs of said local oscillator couplingmeans feed a portion of the local oscillator signal to correspondingones of said second input terminals 15a₂ -15d₂ of respective non-linearelements 15a-15d.

In operation, input signals fed to terminals 113 and 118 are coupled viathe input coupling means 116 and local oscillator coupling means 118 torespective input terminals 15a₁ -15d₁ and 15a₂ -15d₂ of the non-linearelements 15a-15d and produce at the outputs of said elements 15a₃ -15d₃signals having frequency components equal to the sum and difference ofthe input signals, as well as, harmonics of the input signals. Thesignals propagate through one of the pair of two port phase shiftingelements of each one of the output coupling means to provide at a firstone of the output terminals 119a, 119b, an output signal having one ofthe aforementioned frequency components and at the second one of theoutput terminals 119a, 119b, a null or attenuated output signal inaccordance with the relative frequency of the pair of input signals.Radio frequency circuit 110 is a non-distributed, non-successiveinterconnected version of the radio frequency conversion circuit shownin conjunction with FIGS. 1, 7 and 12. By adjusting the electricalpathlengths of the two port phase shifting elements comprising theoutput coupling means 117, input coupling means 116, and localoscillator coupling means 118, any one of the aforementioned radiofrequency conversion circuits, the mixer 10 (FIG. 1), the mixer 60 (FIG.8) and the multiplier 80 (FIG. 12) may be fabricated in anon-distributed version using two port phase shifting elements.

Having described preferred embodiments of this invention, it will now beapparent to one of skill in the art that other embodiments incorporatingits concept may be used. It is felt, therefore, that this inventionshould not be restricted to the disclosed embodiment, but rather shouldbe limited only by the spirit and scope of the appended claims.

What is claimed is:
 1. A radio frequency circuit having first and secondinput terminals fed by first and second input signals having first andsecond frequencies and first and second output terminals comprising:(i)a plurality of nonlinear elements, each having an input electrode and anoutput electrode; (ii) input means, fed by the first input signal havinga first frequency, comprising at least one two port phase shift elementconnected to the first input terminal of the circuit and the inputelectrode of each non-linear element, for providing a phase shiftdifference between portions of said signal coupled to the inputelectrodes of adjacent, successive ones of said nonlinear elements;(iii) means, having a first end coupled to the second one of the inputterminals of the circuit for feeding a second input signal having thesecond frequency to each non-linear element; and (iv) output means,connected between the pair of output terminals of the circuit, forsuccessively electrically connecting the output electrodes of eachnonlinear element; wherein in response to said first and second inputsignals, output signals are provided from said output electrodes andsaid signals propagate in first and second directions along said outputmeans providing first and second output signal portions to provide acomposite output signal at one of said terminals having a frequencycomponent equal to at least a first one of the sum of and differencebetween of the frequencies of said first and second input signals. 2.The circuit of claim 1 wherein the means for feeding the second signalcomprises means for providing substantially identical electricalpathlengths between the second input terminal and each one of theplurality of nonlinear elements.
 3. The circuit of claim 2 wherein thenon-linear elements each comprise a dual-gate field effect transistor.4. The circuit of claim 3 wherein the composite output signal isprovided at a first output terminal when the frequency of the firstsignal is higher than that of the second signal, and said compositeoutput signal is provided at the second output terminal when thefrequency of the first signal is lower than that of the second signal.5. The circuit of claim 4 further comprising:means for selectivelytailoring as a function of frequency the amplitude and phasecharacteristics of each of the output signal portions propagating alongthe output means.
 6. The circuit of claim 5 wherein the signal tailoringmeans comprises at least one capacitor connected between the input meansand a first input electrode of one of the plurality of field effecttransistors.
 7. The circuit of claim 6 wherein the input means furthercomprises:a first plurality of distributed transmission lines, eachhaving a predetermined electrical pathlength; the output coupling meansfurther comprises: a second plurality of distributed transmission lines,each having a predetermined electrical pathlength; and wherein thepredetermined electrical pathlengths of the first and second pluralitiesof distributed transmission lines are selected to impart predeterminedphase shift characteristics to said first and second output signalportions provided from each one of the field effect transistors, toprovide from each of the first output signal portions at first one ofthe first and second output terminals of the circuit, the compositeoutput signal having a frequency equal to a first one of a sum of thefrequencies of the first and second signals and difference between thefrequencies of the first and second signals, and for providing from eachof the second output signal portions at a second one of the first andsecond output terminals said null or attenuated signal.
 8. The circuitof claim 3 further comprising:means for selectively tailoring as afunction of frequency the amplitude and phase characteristics of each ofthe signal portions propagating along the output means.
 9. The circuitof claim 8 wherein the signal tailoring means comprises at least onecapacitor connected between the input means and the input electrode ofeach one of the plurality of nonlinear elements.
 10. The circuit asrecited in claim 1 wherein the nonlinear elements include a second inputelectrode fed by the second input signal; andwherein the means forfeeding the second input signal comprises means for successivelyelectrically interconnecting each one of said second input electrodes tosaid second input terminal, and for providing successively increasingelectrical pathlengths between said input terminal and each successiveone of said second input electrodes.
 11. The circuit of claim 10 whereinthe nonlinear elements each comprise a dual-gate field effecttransistor.
 12. The circuit of claim 11 wherein the composite outputsignal is provided at the first output terminal when the frequency ofthe first signal is higher than that of the second signal, and saidcomposite output signal is provided at the second output terminal whenthe frequency of the first signal is lower than that of the secondsignal.
 13. The circuit of claim 12 further comprising:means forselectively tailoring as a function of frequency the amplitude and phasecharacteristics of each of the signal portions propagating along theoutput means.
 14. The circuit of claim 13 wherein the signal tailoringmeans further comprises at least one capacitor connected between theinput means and a first input electrode of one of the plurality of fieldeffect transistors.
 15. The circuit of claim 14 wherein the input meansfurther comprises:a first plurality of distributed transmission lines,each having a predetermined electrical pathlength; the output meansfurther comprises: a second plurality of distributed transmission lines,each having a predetermined electrical pathlength; and wherein thepredetermined electrical pathlengths of the first and second pluralitiesof distributed transmission lines are selected to impart predeterminedphase shift characteristics to said first and second output signalportions provided from each one of the field effect transistors toprovide from each of the first output signal portions at a first one ofthe first and second output terminals of the circuit, the compositeoutput signal having a frequency equal to a first one of a sum of thefrequencies of the first and second input signals and difference betweenthe frequencies of the first and second input signals, and for providingfrom each of the second output signal portions at a second one of thefirst and second output terminals said null or attenuated signal. 16.The circuit of claim 10 further comprising:means for selectivelytailoring as a function of frequency the amplitude and phasecharacteristics of each of the output signal portions propagating alongthe output means.
 17. A radio frequency circuit having a pair of inputterminals, each fed by one of a pair of input signals and a pair ofoutput terminals comprising:means, including a plurality of transistors,each having a pair of input electrodes and an output electrode,responsive to the pair of input signals for providing a correspondingplurality of output signals having a frequency component related to thefrequency of each input signal; means for providing a composite outputsignal responsive to the pair of input signals, which propagates towardsone of the pair of output terminals in accordance with the difference infrequency between the pair of signals comprising:(i) input means havinga first end connected to a first one of the input terminals of thecircuit for coupling successive portions of the input signal to a firstone of the input electrodes of each transistor, said successive portionshaving a progressively increasing phase shift; (ii) means connected tothe second input terminal of the circuit for coupling a portion of thesecond input signal to a second one of the pair of input electrodes ofeach transistor; and (iii) means, fed by each of said correspondingplurality of output signals, for providing the composite output signal.18. A radio frequency circuit having a pair of input terminals, each fedby one of a pair of signals, and a pair of output terminals,comprising:means, including a plurality of nonlinear elements, eachhaving a pair of input electrodes and an output electrode for providing,in response to the pair of input signals, a corresponding plurality ofoutput signals, each output signal having a frequency component relatedto the frequency of each of the pair of input signals, and means furthercomprising:(i) input means, having a first end connected to a first oneof the pair of terminals of the circuit, for distributively coupling aportion of the first input signal fed to said terminal to a first one ofthe pair of input electrodes of each non-linear element; (ii) meansconnected to a second one of the pair of input terminals of the circuit,for coupling a portion of the second input signal fed to said secondterminal of the circuit to a second one of the pair of input electrodesof each nonlinear element; and (iii) output means, connected between thepair of output terminals of the circuit, for coupling the plurality ofoutput signals from the non-linear elements to provide at a first one ofthe pair of output terminals of the circuit a composite output signalhaving a frequency component related to the frequency of each one of theinput signals, with a second one of the pair of terminals having a nullsignal.
 19. The circuit of claim 18 wherein said input means comprises:adistributed transmission line connected to the input terminal and aplurality of capacitors each one disposed between the input electrode ofeach respective nonlinear element and a portion of the distributedtransmission line to tailor the amplitude and phase characteristics tothe input signals feed to each of the first input electrodes; said meansfor coupling the second signal provides equal electrical pathlengths toeach of said second signal portions fed to the second one of the pair ofinput electrodes of each nonlinear element; and said output meanscomprises a distributed transmission line connected between the pair ofoutput terminals and a plurality of capacitors connected between saidline and a reference potential to increase the electrical pathlength ofsaid distributed transmission line in accordance with the frequency ofsaid signals coupled to the output means.
 20. The circuit as recited inclaim 19 wherein the phase and amplitude characteristics of said signalsfed to the first input electrodes and the phase and amplitudecharacteristics of the output means are selected to provide at the firstoutput terminal the input signal when the frequency of the first inputsignal is higher than the frequency of the second input signal, with anull or attenuated signal at the first output terminal and to provide atthe second output terminal a signal when the frequency of the firstinput signal is lower than the frequency of the second input signal witha null or attenuated signal at the first output terminal.
 21. Thecircuit of claim 20 wherein the nonlinear elements are dual gate fieldeffect transistors and the input electrode are the gate electrodes ofsaid transistors.
 22. The circuit of claim 18 wherein said input meanscomprises a distributed transmission line connected to the inputterminal and a plurality of capacitors each one disposed between theinput electrode of each respective nonlinear element and a portion ofthe distributed transmission line to tailor the amplitude and phasecharacteristics to the input signals fed to the first inputelectrodes,said means for coupling the second signal comprises adistributed transmission line fed by the second signal, which feeds eachof said second input signal portions to said respective nonlinearelements having successively increasing electrical pathlengths to tailorthe phase characteristics to the signals fed to the second inputelectrodes, said output means comprises a distributed transmission lineconnected between the pair of output terminals and a plurality ofcapacitors connected between said line and reference potential toincrease the electrical pathlength of said distributed transmission linein accordance with the frequency of said signals coupled to the outputmeans.
 23. The circuit of claim 22 wherein a first nonlinear element isfed the first input signal with successively nonlinear elements to alast one of said nonlinear elements having progressively increasingphase shifts and the last nonlinear element is fed the second inputsignal with successively nonlinear elements to said first nonlinearelement having progressively increasing phase shifts.
 24. The circuit ofclaim 23 wherein the nonlinear elements are dual gate field effecttransistors and the input electrodes are the gate electrodes of saidtransistors.
 25. A radio frequency mixer circuit having a first inputterminal fed by an input radio frequency signal having a variablefrequency f_(O), a second input terminal fed by a local oscillatorsignal having a known frequency f_(LO) and first and second outputterminals comprising;means for providing at a first one of said firstand second output terminals a first output signal related to a first oneof the sum of the frequencies and difference between the frequencies ofsaid input signal and local oscillator signal, when the frequency of thelocal oscillator signal is greater than the frequency of the inputsignal and a second one of said first and second output terminals afirst one of the sum of the frequency and difference between thefrequencies of said input signal and local oscillator signals when thesignal of the local oscillator signal is less than the frequency of theinput signal said means, further comprising: a plurality of nonlineardevices, each device having first and second input electrodes and anoutput electrode; input means, fed by the input signal comprised of atleast one two port phase shifting element connected to the first inputterminal of the circuit, and comprising means for coupling portions ofsaid input signal to a first input electrode each one of the nonlineardevices, for providing a successively increasing phase shift differencebetween said portions of said signal coupled to successively ones ofsaid input nonlinear devices, means having a first end connected to thesecond input terminal of the circuit for feeding the local oscillatorsignal to the second input electrodes of each nonlinear device; andoutput means connected between the pair of output terminals of thecircuit for successively, electrically connecting the output electrodeof each nonlinear element.
 26. The mixer circuit as recited in claim 25wherein the means for providing first and second output signals furthercomprises means for selectively tailoring as a function of frequency theamplitude and phase characteristics of each of the output signalspropagating along the output coupling means.
 27. The radio frequencymixer circuit of claim 26 wherein each of the plurality of nonlineardevices includes a dual-gate field effect transistor.
 28. The radiofrequency mixer circuit of claim 27 wherein the means for selectivelytailoring comprises a plurality of capacitors coupled between the inputcoupling means and a first input electrode of each one of the fieldeffect transistors, with each of said capacitors having a capacitanceselected to provide amplitude and phase characteristics to input signalscoupled to said field effect transistors, to provide in response at thefirst one of the output terminals and the second one of the outputterminals output signals in accordance with the frequency of the inputsignal relative to the frequency of the local oscillator signal.